It is well-known that industry, government and the general public are aware of the need to preserve and protect the natural environment from the adverse effects caused by polluted industrial effluent which has been, and is currently being, permitted to contaminate the natural environment, particularly rivers and streams where polluted industrial waste water is simply dumped in untreated form. As a result, national and local regulations have been adopted, with increasing strict standards, to reduce or eliminate the undesirable environmental impact of industrial waste, and industry is constantly faced with the problem of meeting the requirements of these regulations while maintaining the cost of waste processing within acceptable limits.
In attempting to meet this challenge, a wide variety of chemical processing is used to treat industrial waste water by causing the impurities therein to react with chemical additives whereby the impurities are reformed as harmless chemical compounds, or the impurities are caused to flocculate so that they can be separated mechanically, as by filtering. Generally, however, many impurities, particularly heavy metals, must be treated separately with different chemical additives, all of which is relatively time consuming and expensive. Additionally, while chemical treating will usually remove the great majority of impurities, it is not uncommon for small, but still undesirable, quantities of the impurities to remain in the water after it has been chemically treated. Finally, it is often necessary to process further the chemically treated water, before it can be added to natural water supplies, to compensate for the adverse effects created by the chemical treatment itself.
Electrolytic cells have been employed to purify waste water utilizing iron or aluminum electrodes in rod or plate form for the production of flocculent precipitates, in the form of iron or aluminum hydroxide, which adsorb impurities in the water. Such techniques are referred to in U.S. Pat. Nos. 3,766,037 and 3,926,754.
A method of treating industrial waste water electrolytically in which the anode comprises one or more aluminum plates or rods, and the cathode comprises one or more iron plates, is disclosed in U.S. Pat. No. 3,783,114. In that patent, aluminum and iron hydroxides aggregate into floc, and adsorb the impurities in the waste water. Floc containing the adsorbed impurities is floated to the surface of the water by bubbles of hydrogen gas formed at the cathode, and is removed from the cell.
Electrodes in rod or plate form used in electrolytic cells to purify waste water tend quickly to become coated by slime generated during the electrolytic process. This results in increased electrical resistance, thereby decreasing the efficiency of the electrolytic treatment. Where aluminum electrodes are employed, the dissolved aluminum tends to form compounds with some of the pullutants in the waste water, forming a coating on the electrodes. In the case of iron electrodes, the iron tends to compound into iron oxides which deposit as a coating on the electrodes. Such "fouling" of the electrodes occurs rapidly in conventional electrolytic treating cells, due to the limited surface areas of the electrodes in plate or rod form. Attempts to overcome this problem have not been notably successful. Chemical wash solutions have been employed to clean the electrodes, and the use of acid solutions or the like in the cells also has been suggested. U.S. Pat. No. 3,769,186 proposes to solve the problem of slime accumulation on aluminum anodes by forming such anodes of an aluminum alloy.
U.S. Pat. No. 3,899,405 discloses a method of removing heavy metals from waste water, in which the cathode comprises a body of particles having tin surfaces. During electrolysis, heavy metal pollutants are deposited upon the particles which become coated and must be regenerated from time to time.